Abstract: To study the driver's understanding of diagrammatic guide signs for interchange, standardize the utility of various graphics, and improve the road traffic environment, a method based on factor analysis was proposed for comprehensively assessing cognition complexity of interchange diagrammatic guide sign. A cognition test, which 37 graphs were designed and three different levels (entire, portion and details of graphs) were covered, was conducted to study the cognition complexity. Data shows that the 37 graphs differ substantially in cognition performance from the three levels. It also depicts that the inconsistency exists in the three levels of visual cognition performance. Seven categories of data, including general graph legibility time, subjective assessment scores, average and maximum value of information read time in three directions, percentage of participants who selected the wrong exit operation and the wrong path, and quantity of risk points, were calculated for composite quantitative assessment by factor analysis technique. The analytical results indicate that the composite scores of graph cognition complexity degree ranges from -1.366 to 2.046, in terms of distribution pattern, and the complexity degree is related to graph features to some degree, as well as element expression mode and utilization degree. The research findings not only can offer a theoretical approach to quantitative evaluation of the complexity and effectiveness of guide signs at interchange, but also provide references for the design and installation of diagrammatic guide signs at interchanges.